Steam generator feedwater preheater

ABSTRACT

Feedwater preheating apparatus for a shell and tube type vapor generator is disclosed incorporating a plurality of nozzles arranged to discharge cold feedwater into a collector conduit disposed in a region of the unit containing heated fluid. Inductor means are provided to aspirate heated fluid into the collector conduit for mixing with the feedwater whereby the latter is heated.

United States Patent Romanos May 9, 1972 [54] STEAM GENERATOR FEEDWATERPREHEATER [72] Inventor:

[73] Assignee:

Nicholas D. Romanos, Chattanooga, Tenn.

Combustion Engineering Inc., Windsor, Conn.

[22] Filed: Dec. 31, 1970 [21] Appl.No.: 103,188

[52] U.S. Cl ....122/34, 122/438 [51] Int. Cl ..F22b 1/16 [58] FieldolSearch ..l22/32,34,438

[56] References Cited UNITED STATES PATENTS 2,862,479 12/1958 Blaser etal. ..122/34 Coykendall 122/438 X Sprague 122/32 PrimaryExaminer-Kenneth W. Sprague Attorney-Carlton F. Bryant, Eldon H. Luther,Robert L. 01- son, John F. Carney, Richard H. Berneike, Edward L.Kochey, Jr. and Lawrence P. Kessler [57] ABSTRACT Feedwater preheatingapparatus for a shell and tube type vapor generator is disclosedincorporating a plurality of nozzles arranged to discharge coldfeedwater into a collector conduit disposed in a region of the unitcontaining heated fluid. Inductor means are provided to aspirate heatedfluid into the collector conduit for mixing with the feedwater wherebythe latter is heated.

14 Claims, 4 Drawing Figures PATENTEDMAY 9 I972 SHLET 2 OF 2 VEN T02N/CHOI. AS A? ROM N0 5 A Tree/v5 Y STEAM GENERATOR FEEDWATER PREI'IEATERBACKGROUND OF THE INVENTION In the operation of shell and tube .vaporgenerators vaporizable liquid is placed in indirect heat exchangerelation with a heated fluid. Conventionally, the heated fluid isconducted through tubes that are housed within a pressure shell with thevaporizable liquid being admitted to the shell in a manner to immersemost or all of the tube surface. In units of the prior art a cylindricalbaffle is disposed about the bundle of tubes to divide the shellinterior to an annular downflow passage with which the vaporizableliquid supply means communicates and an axially disposed evaporatorchamber containing the bundle of tubes.

Because the feed liquid that is admitted to the downflow passage is at aconsiderably lower temperature than the vaporizable fluid flowing in theevaporator chamber and still lower than that of the heated fluidconducted by the tubes, means must be provided to counter the affectsproduced by the admission of this cold liquid. These affects includeinstabilities in the generation of vapor in local areas of theevaporation chamber, the creation of thermal gradients in critical areasof the tube-sheet-to-shell welded joints, and the aggravation of thermalexpansion differential between the tubes and the cylindrical baffle.

It is well known that such problems can be alleviated by preheating thefeed liquid prior to admitting it to the vapor generator and,particularly, prior to passing it to the evaporation chamber thereof.Such preheating has, in the past, been accomplished by the use ofseparate heat exchangers located externally of the unit to heat the feedliquid prior to its admission to the shell. Alternatively, reliance hasbeen made upon the mixture in the downflow passage of the incoming feedliquid with liquid being recirculated through the unit, the latter beingat about saturation temperature, for preheating purposes.

Neither of these alternatives has been found to be completelysatisfactory. The first-mentioned considerably increases the equipmentcosts of the vapor generating plant in that supplementary heat exchangeapparatus is required while the latter suffers from the deficiency ofdisuniformity of preheating due to variances occuring in the amount ofliquid recirculated at different levels of unit operation.

It is to the solution of these problems, therefore, that the presentinvention is directed.

SUMMARY OF THE INVENTION According to the invention, apparatus that isintegral with a shell and tube vapor generator is provided forpreheating the feed liquid admitted to the same by the transfer of heatfrom the vapor-liquid mixture generated within the vapor generator. Theinvention contemplates providing a plurality of feedwater dischargenozzles disposed in a region of the vapor generator containing heatedvapor-liquid mixture. The nozzles are arranged to discharge feedwaterinto a collector conduit and inductor means that cooperate with thenozzles are provided to aspirate a portion of the vapor-liquid mixtureinto mixed relation with the feedwater within the collector conduitwhereby the latter is heated by the transfer of heat between the twofluids.

The invention also contemplates a novel baffle arrangement forconducting the heated feedwater from the collector conduit to thedownflow passage in a manner whereby it will be distributedsubstantially uniformly about the periphery of the downflow passage.

For a better understanding of the invention its operating advantages andthe specific objectives obtained by its use, reference should be made tothe accompanying drawings and descriptions which relate to the preferredembodiment.

DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevational section 'of shelland tube type vapor generator incorporating the present invention;

FIG. 2 is a partial elevational section of a portion of the vaporgenerator shown in FIG. 1;

FIG. 3 is a section taken along line 3-3 of FIG. 2; and

FIG. 4 is a section taken along line 4-4 of FIG. 2.

DESCRIPTION OF PREFERRED EMBODIMENT In FIG. 1 of the drawings there isshown a shell and tube type vapor generator 10 incorporating feedwaterpreheating apparatus constructed according to the present invention. Thevapor generator 10 comprises a vertically elongated pressure vesseldefined by a lower cylindrical shell 12 and an enlarged diameter, uppercylindrical shell 14 that is integrally connected to the lower shell bymeans of a frusto-conical transition member 16. The ends of the vesselare closed, at the bottom by means of a hemispherically-formed closurehead 18 and at the top by a dome shaped closure 20 containing a vaporoutlet nozzle 22. The interior of the pressure vessel contains anaxially elongated cylindrical baffle 24 that is concentrically spacedfrom the wall of the lower shell 12 to define an inner evaporationchamber 30 and an external, annular downcomer flow passage 32. The lowerend of the baffle 24 is spaced from the bottom of the vessel interior inorder to establish fluid communication between the downflow passage 32and the evaporation chamber 30. The bottom of the vessel interior isdefined by a tube sheet 34 that extends transversely of the axis of thevessel and connects with the wall of the shell 12. The tube sheet 34contains a plurality of openings to fixidly secure the ends of U-shapedheat exchange tubes 38 that are arranged to form an axially extendingbundle substantially filling a transverse section of the evaporationchamber 30. The tube openings extend through the tube sheet 34 to placethe tubes 38 in fluid communication with a heating fluid chamber 42 thatoccupies that region of the vessel enclosed by the closure head 18 andthe tube sheet 34. This chamber 42 is divided into inlet and outletportions, 44 and 46 respectively, by means of a divider plate 48 thatextends transversely of the chamber and is weldedly attached to the tubesheet 34 and the inner surface of the closure 18. The tubes 38 of thetube bundle are arranged such that their opposite ends communicate withone of the respective portions of the chamber 42 whereby the circulationof heating fluid through the tubes is effected. lnlet and outletnozzles, 50 and 52 respectively, communicate with the respective chamberportions 44 and 46 and connect the same to a source of heating fluid(not shown) in order to effect continous circulation of heating fluidbetween the vapor generator and the source.

According to the invention, novel means are provided for supplyingfeedwater to the vapor generator 10 and for preheating the same prior toits discharge into the downflow passage 32 for ultimate entry into theevaporation chamber 30. Such means comprises a feedwater inlet nozzle 54that penetrates the upper vessel shell 14 and an inlet duct 56 thatcommunicates therewith, the latter extending horizontally across theinterior of the vessel as shown in FIG. I. The duct 56 is disposedwithin a region of the vapor generator termed the vapor collectionplenum 58 that is formed in the upper region of the vessel interior inopen communication with the evaporation chamber 30. The plenum isdefined by an enlarged diameter cylindrical baffle 60 which isconcentrically spaced from the upper end of the downflow baffle 24 thusto form concentric spaces therebetween indicated as feedwater dischargespace 62 and separated liquid recirculation passage 64. The top of theplenum 58 is closed by a horizontally disposed closure plate 66. Theplate 66 contains a plurality of mutually spaced openings 68 to whichare attached centrifugally operated vapor-liquid separating apparatus 70of wellknown construction. The plenum-forming members are secured attheir upper and lower ends to the interior surface of shell 14 and tothe bafile 24 respectively by appropriate slip joints 72 and 74 that arecapable of accommodating relative thermally-induced radial and axialexpansion and contraction of the respective members.

Adjacent its lower end the vapor collection plenum 58 is provided withan annular distribution channel 76 formed of concentric annular platesthat are arranged to separate the channel from the remainder of theplenum. These plates include a frusto-conical plate 78 forming the innerperipheral side of the channel and a top closure plate 80 extending fromthe top of plate 78 to the annular wall of baffle plate 60. The lowerend of the channel is provided with concentrically spaced, axiallydisposed plates 82 and 84 and, together with horizontally arrangedclosure plates 86 and 88, form a wierlike tortuous passage thatcommunicates, at 90 with the feedwater discharge space 62.

As shown in the drawings the feedwater inlet duct 56 may be flared atits outer end and attached, as by means of welding, to the inner wall ofthe nozzle 54. The duct 56 is preferably formed of a lesser diameterthan the nozzle wall to extend spacedly therethrough to provide athermal shield for protecting the shell against undue stressing thatwould otherwise be caused by the impingement of the incoming cold liquidupon the hotter metal members. The duct 56, whose inner end is closed bya closure cap 92, extends diametrally across the plenum 58 terminatingshort of baffle 60 and extending through openings 94 provided infrusto-conical channel-forming plate 78 for reasons hereinafterdescribed. An enlarged diameter feedwater collection conduit 96surrounds the feedwater duct 56 in eccentric relation thereto. Theconduit is substantially extensive with the duct through the plenum 58having its ends supportedly attached, as by welding or the like, to thebaffle 78 and plate 80.

A plurality of upstanding discharge tubes or nozzles 98 are axiallyspaced along the length of duct 56. These tubes extend upwardly from theduct and through the accommodating openings 100 provided in the conduit96 to locate the upper, discharge ends of the tubes within the vaporcollection plenum 58. inductor caps 102 spacedly enclose, by means ofradial struts 104, the discharge end of each tube 98. Each inductor cap102 is, as shown, a generally cylindrical member having a hollowinterior that spacedly encircles the upper end of the tube to form anannular passage 106 thereabout. The base 107 of the interior of the cap102 is provided with a spherical or equivalent shape to smoothlyredirect the stream of feedwater issuing from the tube downwardlythrough the passages 106 and thence through the openings 100 into thefeedwater collector conduit 96. The passage 106 between the upper end ofeach discharge tube and the wall of its associated cap is sized tocreate a relatively high velocity flow of liquid from the passage intothe conduit interior thereby creating a region of low pressure adjacenteach conduit opening 100 that is effective to aspirate amounts of heatedvapor-liquid mixture from the plenum 58 into the conduit. Within theconduit interior the inducted higher temperature heated fluid isintimately -mixed with the cold feedwater thereby increasing thetemperature of the latter.

As in the disclosed arrangement, a liquid difiusor plate 108, here shownattached to each tube 98, may be provided to obstruct the flow of liquidentering the interior of conduit 96 causing the liquid stream to bediffused into droplets by impinging on the plate. in this way the liquidcan be dispersed into small droplets thereby presenting a greater amountof surface area to the other heat exchange medium by which heat transferbetween the two will be enhanced.

The operation of the hereindescribed vapor generating apparatus is asfollows. A high temperature high pressure heating fluid flows from itssource through the inlet nozzle 50 into the inlet portion 44 of thechamber 42 and then is conducted by means of the tubes 38 through theevaporation chamber 30 emerging therefrom through the outlet portion 46of the chamber 42 and nozzle 52. At the same time, feedwater isconducted to the interior of the vessel through inlet nozzle 54 andinlet duct 56. The feedwater, after having been preheated as describedhereinafter, is conducted downwardly through the down flow passage 32,entering the evaporation chamber 30 at the bottom thereof, and beingcaused to flow upwardly through the chamber 30 in heat exchange relationwith the heating fluid conducted through tubes 38 due to the thermalsiphonic action occuring therein as a result of the difference indensity of the fluid in the downflow passage 32 and the evaporationchamber 30. In flowing through the evaporation chamber 30 the liquid isheated and a portion thereof transformed into vapor. The so-createdvapor-liquid mixture rises into the vapor collection plenum 58 and issubsequently caused to flow through the several separating apparatus 70where the component parts of the mixture are separated by centrifugalaction. The separated vapor rises from the separator 70 into the upperregion of the vessel and is conducted therefrom through the vapor outletnozzle 22. The separated liquid, on the other hand, is dischargeddownwardly into the liquid recirculation passage 64, ultimately enteringthe downflow passage 32 and recirculated through the unit.

The feedwater that enters the unit through the inlet duct 56 ispreheated as hereinbefore more fully described by mixing in thefeedwater collection conduit 96 with a portion of the vapor-liquidmixture that is aspirated from the vapor collection plenum 58 into theconduit by means of the action of the inductor caps 102. The heatedfeedwater is conducted from the opposite ends of the conduit 96 into theannular distribution channel 76 within which the liquid is dispersedannularly about the periphery of the channel due to the presence of thewier-like structure presented by the plate member 82 through 88. Theliquid is discharged downwardly from the channel 76 through the annularopening into the feedwater discharge space 62 where it will be caused tocomingle with the separated liquid flowing through the passage 64 priorto entering the downflow passage 32. in mixing with the separated liquidwhich exists at saturation temperature, the heated feedwater, if stillsubcooled, will have its temperature further raised before entering thepassage 32. The combined flows of fresh feedwater and recirculatedliquid enters the evaporation chamber 30 at the bottom of the downflowpassage 32 and circulates through the unit in the manner heretoforedescribed.

By means of the present invention, therefore, there is provided aeffective means for preheating feedwater supplied to shell and tube typevapor generators thus to ameliorate the deficiencies in vapor generatoroperation attendant with supplying unheated feedwater to such apparatus.The preheating equipment is simple in configuration and requires little,if any, change in the design of present day vapor generators toaccommodate its use. Moreover, the apparatus can be constructed atlittle expense using components that are readily available.

It will be understood that various changes in the detail, materials, andarrangement of parts have been herein described and illustrated inorderto explain the nature of the invention may be made by those skilled inthe art within the principle and scope of the invention as expressed inthe appended claims.

What is claimed is:

1. In a vapor generator wherein vapor is produced by the transfer ofheat between a fluid heating medium and a vaporizable liquid and whereinthe vapor produced is contained in a vapor collection plenum, theimprovement comprising apparatus for preheating feedwater supplied tosaid vapor generator prior to passing it in heat exchange relation withsaid heating medium, said apparatus including:

a. a mixing chamber disposed in, but substantially isolated from, saidvapor collection plenum;

b. an inlet duct connected to a source of feedwater;

c. a plurality of discharge tubes emanating from said duct and arrangedto discharge incoming feedwater into said mixing chamber;

d. inductor means operated by the flow of feedwater from said dischargetubes for aspirating heated vaporizable liquid from said vaporcollection plenum into said mixing chamber in mixed relation with saidfeedwater; and

e. means for conducting heated feedwater from said mixing chamber intoheat exchange relation with said heating medium.

2. Apparatus as recited in claim 1 wherein the outlet ends of saiddischarge tubes are disposed externally of said mixing chamber in saidvapor collection plenum and the wall of said mixing chamber containsmeans forming openings to receive the feedwater discharge from saiddischarge tubes.

3. Apparatus as recited in claim 2 wherein said mixing chamber comprisesa horizontally disposed, transversely extending conduit enclosing saidinlet duct and said discharge tubes extend from said duct through themixing chamber wall openings to dispose their outlet ends in said vaporcollection plenum, and inductor means operative to aspirate heatedvaporizable liquid into said mixing chamber by directing the flow offeedwater from the outlet ends of said discharge tubes through saidconduit opening.

4. Apparatus as recited in claim 3 wherein said inductor means compriseannular hollow caps spacedly enclosing the outlet ends of said dischargetubes, the interior wall of said caps defining a flow directing surfacefor conducting the discharged feedwater through said conduct openings.

5. Apparatus as recited in claim 4 wherein the interior of said inductorcaps is formed of a substantial U-shaped section.

6. In a vertically disposed shell and tube vapor generator comprising:

a. generally cylindrical sell means defining a pressure vessel having alower vapor generating portion and a vapor collection plenum disposed inopen communication thereabove;

b. a vapor outlet from said vapor collection plenum;

c. an axially extending conduit concentrically spaced from the wall ofsaid shell to define an annular downflow passage about said vaporgenerating portion;

d. means for circulating fluid heating medium through said vaporgenerating portion;

e. means for circulating vaporizable liquid seriatim through saiddownflow passage, said vapor generating portion and said vaporcollection plenum;

f. the improvement comprising feedwater preheater apparatus including:

i. a horizontally disposed conduit traversing said vapor collectionplenum defining a mixing chamber;

ii. means forming a plurality of longitudinally spaced openings in saidconduit communicating said mixing chamber with said vapor collectionplenum;

iii. a plurality of feedwater discharge tubes having their outlet endsarranged to discharge feedwater through said openings into said mixingchamber;

iv. inductor means operated by the flow of feedwater from said dischargetubes for aspirating heated vaporizable liquid from said collectionplenum into said mixing chamber; and

v. means for conducting heated feedwater from said mixing chamber intosaid downflow passage.

7. Apparatus as recited in claim 6 including:

a. a feedwater inlet nozzle penetrating said shell;

b. an inlet duct having one end communicating with said nozzle, saidduct being enclosed by said mixing chamber conduit and substantiallycoextensive therewith; and

c. said feedwater discharge tubes connecting with said duct and havingtheir outlet ends extending through said conduit openings into saidvapor collection plenum.

8. Apparatus as recited in claim 7 wherein the periphery of said conduitopenings is concentrically spaced about the surface of the respectivefeedwater discharge tubes.

9. Apparatus as recited in claim 8 wherein said inductor means eachcomprise:

a. generally cylindrical, hollow cap spacedly enclosing the outlet endof an associated feedwater discharge tube;

b. the interior of said cap defining a flow directing surface fordirecting feedwater from said discharge tube through said concentricconduit opening.

10. Apparatus as recited in claim 9 wherein said inductor cap issubstantially U-shaped in section.

11.A aratus as recited in claim6including: a. b e means defining anannular distribution channel about said vapor collection plenum, saidbaffle means including concentrically spaced baffles defining a tortuouspath;

b. means defining an annular opening connecting said channel with saiddownflow passage; and

c. means connecting said mixing chamber in fluid communication with saiddistribution channel.

12. Apparatus as recited in claim 11 wherein the opposite ends of saidmixing chamber conduit are open and connect with said baffle means, saidbaffle means including openings to connect the ends of said mixingchamber conduit in fluid communication with said distribution channel.

13. Apparatus as recited in claim 11 including:

a. an annular plate concentrically spaced from said shell to define saidvapor collecting plenum on its interior and an annular recirculatingliquid-flow passage thereabout;

b. a horizontal plate closing the top of said plenum;

c. a plurality of separators mounted upon said horizontal plate in fluidcommunication with said plenum. and arranged to discharge separatedliquid into said recirculating liquid flow passage.

14. Apparatus as recited in claim 13 wherein the lower end of saidannular plate cooperates with said concentric baffles to concentricallyspace said distribution channel opening from said recirculating liquidflow passage, said plate terminating short of said downflow passage toplace said opening and said liquid flow passage in fluid communicationwith said downflow passage.

1. In a vapor generator wherein vapor is produced by the transfer ofheat between a fluid heating medium and a vaporizable liquid and whereinthe vapor produced is contained in a vapor collection plenum, theimprovement comprising apparatus for preheating feedwater supplied tosaid vapor generator prior to passing it in heat exchange relation withsaid heating medium, said apparatus including: a. a mixing chamberdisposed in, but substantially isolated from, said vapor collectionplenum; b. an inlet duct connected to a source of feedwater; c. aplurality of discharge tubes emanating from said duct and arranged todischarge incoming feedwater into said mixing chamber; d. inductor meansoperated by the flow of feedwater from said discharge tubes foraspirating heated vaporizable liquid from said vapor collection plenuminto said mixing chamber in mixed relation with said feedwater; and e.means for conducting heated feedwater from said mixing chamber into heatexchange relation with said heating medium.
 2. Apparatus as recited inclaim 1 wherein the outlet ends of said discharge tubes are disposedexternally of said mixing chamber in said vapor collection plenum andthe wall of said mixing chamber contains means forming openings toreceive the feedwater discharge from said discharge tubes.
 3. Apparatusas recited in claim 2 wherein said mixing chamber comprises ahorizontally disposed, transversely extending conduit enclosing saidinlet duct and said discharge tubes extend from said duct through themixing chamber wall openings to dispose their outlet ends in said vaporcollection plenum, and inductor means operative to aspirate heatedvaporizable liquid into said mixing chamber by directing the flow offeedwater from the outlet ends of said discharge tubes through saidconduit opening.
 4. Apparatus as recited in claim 3 wherein saidinductor means comprise annular hollow caps spacedly enclosing theoutlet ends of said discharge tubes, the interior wall of said capsdefining a flow directing surface for conducting the dischargedfeedwater through said conduct openings.
 5. Apparatus as recited inclaim 4 wherein the interior of said inductor caps is formed of asubstantial U-shaped section.
 6. In a vertically disposed shell and tubevapor generator comprising: a. generally cylindrical sell means defininga pressure vessel having a lower vapor generating portion and a vaporcollection plenum disposed in open communication thereabove; b. a vaporoutlet from said vapor collection plenum; c. an axially extendingconduit concentrically spaced from the wall of said shell to define anannular downflow passage about said vapor generating portion; d. meansfor circulating fluid heating medium through said vapor generatingportion; e. means for circulating vaporizable liquid seriatim throughsaid downflow passage, said vapor generating portion and said vaporcollection plenum; f. the improvement comprising feedwater preheaterapparatus including: i. a horizontally disposed conduit traversing saidvapor collection plenum defining a mixing chamber; ii. means forming aplurality of longitudinally spaced openings in said conduitcommunicating said mixing chamber with said vapor collection plenum;iii. a plurality of feedwater discharge tubes having their outlet endsarranged to discharge feedwater through said openings into said mixingchamber; iv. inductor means operated by the flow of feedwater from saiddischarge tubes for aspirating heated vaporizable liquid from saidcollection plenum into said mixing chamber; and v. means for conductingheated feedwater from said mixing chamber into said downflow passage. 7.Apparatus as recited in claim 6 including: a. a feedwater inlet nozzlepenetrating said shell; b. an inlet duct having one end communicatingwith said nozzle, said duct being enclosed by said mixing chamberconduit and substantially coextensive therewith; and c. said feedwaterdischarge tubes connecting with said duct and having their outlet endsextending through said conduit openings into said vapor collectionplenum.
 8. Apparatus as recited in claim 7 wherein the periphery of saidconduit openings is concentrically spaced about the surface of therespective feedwater discharge tubes.
 9. Apparatus as recited in claim 8wherein said inductor means each comprise: a. generally cylindrical,hollow cap spacedly enclosing the outlet end of an associated feedwaterdischarge tube; b. the interior of said cap defining a flow directingsurface for directing feedwater from said discharge tube through saidconcentric conduit opening.
 10. Apparatus as recited in claim 9 whereinsaid inductor cap is substantially U-shaped in section.
 11. Apparatus asrecited in claim 6 including: a. baffle means defining an annulardistribution channel about said vapor collection plenum, said bafflemeans including concentrically spaced baffles defining a tortuous path;b. means defining an annular opening connecting said channel with saiddownflow passage; and c. means connecting said mixing chamber in fluidcommunication with said distribution channel.
 12. Apparatus as recitedin claim 11 wherein the opposite ends of said mixing chamber conduit areopen and connect with said baffle means, said baffle means includingopenings to connect the ends of said mixing chamber conduit in fluidcommunication with said distribution channel.
 13. Apparatus as recitedin claim 11 including: a. an annular plate concentrically spaced fromsaid shell to define said vapor collecting plenum on its interior and anannular recirculating liquid flow passage thereabout; b. a horizontalplate closing the top of said plenum; c. a plurality of separatorsmounted upon said horizontal plate in fluid communication with saidplenum and arranged to discharge separated liquid into saidrecirculating liquid flow passage.
 14. Apparatus as recited in claim 13wherein the lower end of said annular plate cooperates with saidconcentric baffles to concentrically space said distribution channelopening from said recirculating liquid flow passage, said plateterminating short of said downflow passage to place said opening andsaid liquid flow passage in fluid communication with said downflowpassage.